Melanism has been known as the major cause of freckles such as chloasma and melasma, and its therapy has been deemed very difficult.
Fragrance Journal, Vol. 63, pp. 40-44 (1983) reports that kojic acid (5-oxy-2-oxymethyl-.gamma.-pyrone) is effective in suppressing and removing subcutaneous pigmentation, as well as proposes an external application of a cream composition containing kojic acid.
It is, however, very difficult to attain the expected therapeutic effect with such external application in a short period of time because of the limited amount of kojic acid that can be externally administered.
The present inventor investigated various means to remove pigmentation, and disclosed in Japan Patent Kokai Nos. 121963/83, 124457/83, 124458/83 and 124459/83 that subcutaneous absorption of a vitamin effective in removing pigmentation, specifically, vitamin C, is accelerated by iontophoresis.
My attempt to remove pigmentation by iontophoresis of kojic acid has proved unsatisfactory.
Further study shows that kojic acid does not form an effective amount of ion because its acid dissociation constants in aqueous solution, pKa, are relatively high, i.e. 7.90 and 8.03.